Overnight Fluid Boluses For A “Low MAP”

2 AM: “Hey doc, the patient’s MAP (mean arterial pressure) has been in the high 50s for the last hour. Urine output isn’t that great either. Wanna bolus some fluid?”

This knee-jerk reaction is a practice that needs to change! Admittedly, some of it is driven by protocol and also seeing numbers improve (transiently) after fluid administration. However, we need to understand the problem with habitually bolusing fluid each time a patient’s urine output decreases, their MAP is low, they pick their nose, or they listen to Taylor Swift. Oh yeah, I went there! 😉

If an asymptomatic patient is tolerating enteral feeds with no significant ongoing losses (ie, large burn injuries, hemorrhage, diarrhea, etc.), I’m very reluctant to incessantly chase numbers overnight with fluids. Even in healthy patients, the majority of a fluid bolus will move out of the vessels within an hour. Now imagine if you’re critically ill with any degree of capillary leak. Studies really aren’t showing conclusive, sustained benefit with albumin either. Human physiology is built to deal with intermittent bouts of hypovolemia but not really hypervolemia from IV fluids.

The name of the game is to improve oxygen delivery (flow) and oxygen uptake/utilization at the cellular level. Fluid administration may transiently increase cardiac output while diluting hematocrit. So what did you really gain besides glycocalyx damage, tissue congestion, and a volume load that may not be mobilized as readily (ie, a failing right heart).

The growing evidence supporting the safe administration of vasopressors peripherally (something I do all the time as an anesthesiologist) may change the culture from a “fluid first” to an “afterload first” approach in the coming years.

Drop me a comment with your thoughts!

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  1. Could you write an article elaborating on fluid administration and glycocalyx damage? I listened to an episode of the ACRACC where they discussed it briefly, but am still trying to fully grasp it and how it plays out in my daily clinical practice.

    • Hey Cameron! Check out what I’ve written here on the glycocalyx. As far as how it plays into your practice, I think it just goes to show that crystalloids really are not “just water” or “IV hydration” like we once thought they were. Using liters upon liters in the OR can spell trouble post-operatively that we often don’t see until the patient is transferred out of the PACU. I know during residency, if you compare how I did the same case CA-1 year versus chief year, I probably used half as much fluid, way less paralytic, etc. at the end of residency.


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